Washington, Jan 18 : Scientists have reported the discovery of a strong variation in the tectonic stresses in Nankai Trough - a region of the Pacific Ocean notorious for generating devastating earthquakes and tsunamis in southeastern Japan.

The Nankai Trough is known as a subduction zone, because it marks the place where one tectonic plate slides beneath another. ectonic plates are pieces of the Earth's crust, and earthquakes often occur in regions like subduction zones where plates grate and rub against one another.

For some unknown reasons, plates that should move smoothly relative to each other sometimes become locked. In spite of this, the plates continue moving and stress builds at the points where the plates are locked.

The stored energy at these sites is eventually released as large earthquakes, which occur when the locked area breaks and the plates move past one another very rapidly, creating a devastating tsunami like the one in Sumatra and the Indian Ocean three years ago.

Using the new scientific drilling vessel "Chikyu," the team drilled deep into a zone responsible for undersea earthquakes that have caused tsunamis. They collected physical measurements and images using new rugged instruments designed to capture scientific data from deep within a well while it is being drilled.

The drilling, done by Rice University Earth scientist Dale Sawyer and colleagues, marked the beginning of this massive project, which IODP (Integrated Ocean Drilling Program) has dubbed the Nankai Trough Seismogenic Zone Experiment, or NanTroSEIZE.

In addition to the objective of drilling across the plate boundary fault, NanTroSEIZE scientists also hope to sample the rocks and fluids inside the fault, and they are aiming to place instruments inside the fault zone to monitor activity and conditions leading up to the next great earthquake.

According to Sawyer, scientists with the IODP plan to return to the Nankai Trough aboard the Chikyu each year through 2012, with the ultimate goal of drilling a six-kilometer-deep well to explore the region where the quakes originate.

If they succeed, the well will be more than three times deeper than previous wells drilled by scientific drill ships, and it will provide the first direct evidence from this geological region where tsunami-causing quakes originate.